1. Field of Invention
This invention relates to treatment of aneurysms.
2. Review and Limitations of the Prior Art
An aneurysm is an abnormal localized bulging or ballooning of the wall of a blood vessel. A cerebral aneurysm is an abnormal bulging or ballooning of an intercerebral artery. The prevalence of cerebral aneurysms is in the range of 1-5%.
According to the National Institute of Neurological Disorders and Stroke (NINDS) of NIH, the incidence of reported ruptured aneurysms is about 10 per 100,000 persons per year (about 27,000 per year in the U.S.). Approximately one third to one half of people who suffer a ruptured cerebral aneurysm die within one month and, among those who survive, approximately one half suffer significant deterioration of brain function. The vast majority of cerebral aneurysms form in the junction of arteries known as the Circle of Willis where arteries come together and from which these arteries send branches to different areas of the brain.
The most common methods of treating aneurysms are surgical clipping (placing a clamp on the aneurysm from outside the vessel) and endovascular coiling (inserting flexible coils into the aneurysm from inside the vessel). During the past three decades, there has been a general trend away from surgical clipping and toward less-invasive endovascular methods of treating aneurysms such as coiling. The limitations of surgical clipping include the risks of invasive surgery and difficulty accessing aneurysms in some areas. We will now discuss endovascular coiling in greater depth because the invention disclosed here is more similar to coiling than to clipping. The following are four serious problems with endovascular coiling in the prior art that will be corrected by the present invention:
1. Limited Fill Volume Due to Resilient and Springy Coils
Endovascular coils in the prior art tend to be relatively resilient and springy. They are often metal. These qualities are needed in traditional coiling in order to create the surface tension between the coils and the aneurysm walls that holds the coils within the aneurysm sack. The coil loops do not form a solid mass within the aneurysm and would likely prolapse into the parent vessel if they were not resilient and springy. However, the resilient and springy nature of coils in the prior art limits the percentage of the aneurysm volume that can be filled by these coils. As these coils overlap in loops, there are often large gaps between them. Fill rates for the aneurysm sack volume can be as low as 25%-50%. Much of the volume of the aneurysm remains unfilled. As a result of these low fill rates, sometimes blood can continue to flow into the aneurysm and the aneurysm can continue to expand or even rupture.
2. Limited Fill Volume Due to Radially Inward Filling Process
In deployment of the endovascular coils in the prior art, accumulation of coil mass starts around the perimeter of the aneurysm. Accumulation of mass then moves radially-inward toward the center of the aneurysm sack with successive coil loops. Unfortunately, coil maneuverability can become quite constricted as the remaining central volume shrinks. Visibility can also be difficult inside the hollow ball of perimeter coils. Accordingly, it can be difficult to achieve a high percentage of fill volume inside the mass of coils and for the aneurysm overall. As a result, the mass of coils can be relatively hollow and the coils can compact over time. This can allow recanalization of the aneurysm, continued aneurysm expansion, and even aneurysm rupture.
3. Coil Prolapse Due to Randomness of Coil Loop Directions
In deployment of endovascular coils in the prior art, the directionality of looping within the aneurysm during coiling is constantly changing, highly variable, and somewhat random in nature. Although a talented and experienced practitioner can exert some control over the changing directionality of coil looping by manipulating the device from outside the patient's body, it can be laborious for the practitioner to constantly work at avoiding having the loops turn in a direction that could prolapse into the parent vessel. Coil loops that prolapse into the parent vessel can block blood flow in real time. Prolapsed coils can also cause embolization or stoke in the future.
4. Long Procedure Time Due to Randomness of Coil Loop Directions
In addition to the possibility of coil prolapse into the parent vessel due to the randomness of changing loop directionality in traditional endovascular coiling, this randomness also makes the procedure time consuming. It can be very time-consuming for a practitioner to gradually snake coils around the aneurysm, one loop at a time, in different directions. This is especially true when multiple coils are used or when coils with different characteristics are used at different stages in the procedure.
For these four reasons, despite significant progress in surgical clipping and endovascular coiling during the past two decades, there remains a significant unmet clinical need for development of a new option to treat cerebral aneurysms that can address these four problems. The invention that we will now disclose is a novel option for treating cerebral aneurysms that can address these four problems and meet this unmet clinical need.